Apparatus for the generation of laser radiation

ABSTRACT

An apparatus for the generation of laser radiation according to the invention comprising a discharge chamber of essentially rectangular cross section made from insulating material, one pair of discharge electrodes between which a gas discharge initiated by UV preionization arising from a corona discharge can be produced in a direction transverse to an optical resonator, as well as a charging and discharging circuit and a gas circulation and cooling system. The two opposite walls of the discharge chamber on which the electrodes are arranged are provided with a metal coating, e.g. metal plates of sheets. The remaining lateral walls of the discharge chambers are provided with conducting structures, preferably wire grids which are insulated against the interior space and extend up to the level of the metal coating.

The present invention relates to an apparatus for the generation oflaser radiation consisting of a discharge chamber of essentiallyrectangular cross section made from insulating material, one pair ofdischarge electrodes between which a gas discharge initiated by UVpreionization arising from a corona discharge can be produced in adirection transverse to the optical resonator; as well as a charging anddischarging circuit and a gas circulation and cooling system.

Transversely excited pulsed lasers operate preferably at atmosphericpressure and are known as TEA (transversely excited atmosphericpressure) lasers. These lasers have a high efficiency and good radiationproperties, provided that the excitation covers the whole volume betweenthe electrodes and does not contract into sparks. Uniform discharge canbe achieved by preionization of the laser gas using double pulsedischarge technics or by electron beam or UV light, the UV lightoriginating in a corona discharge. It also known that special devicesfor preionization are unnecessary if metal parts of the structure areled along one electrode such that they are insulated from the electrodebut have the potential of the couterelectrode (Optical Engineering 15(1976) 17-19, H. JETTER, K. Gurs, DE-OS 31 18 868). In this case, too, acorona discharge is initiated which emits UV light. In the laseraccording to DE-OS 31 18 868, two electrodes are arranged opposite toeach other, between which the laser gas flows. This permits laseroperation at high pulse repetition frequency. The lower electrode isheld by insulated rods which at the same time serve for power supply.They are mounted along the upper electrodes and have the potential ofthe lower electrode, thus permitting corona discharge. A drawback ofthis setup is the relatively high technical effort involved in the useof metal rods for mounting the second electrode and the safe insulationof the rods against the first electrode.

The aim of the present invention therefore is to develop a TEA laser ofhigh pulse frequency which does not involve the drawbacks ofconventional setups and permits preionisation by corona discharge withvery low technical effort.

According to the present invention, this problem is solved by providingthe two opposite walls of the discharge chamber carrying the electrodeswith a metal coating and the remaining lateral walls of the dischargechamber with conducting structures which are insulated against theinterior space and extend on both sides up to the level of the metalcoating.

The invention is explained on the basis of the attached schematicdrawings, wherein

FIG. 1 shows a section of the discharge chamber provided with metalcoatings and conducting structures, in a direction transverse to theresonator axis;

FIG. 2 shows a lateral view of the system with a possible arrangement ofthe conducting structures;

FIG. 3 shows the setup according to FIG. 1 with the adjacent gascirculation and cooling system;

FIG. 4 shows a possible embodiment of the partition wall between thedischarge chamber and the gas circulation and cooling system; and

FIG. 5 shows another embodiment where the gas circulation and coolingsystem and the discharge chamber form two separate gas-tight connectedunits.

According to the invention, a laser chamber 1 with essentially square orrectangular cross section is used. Two opposite walls of the dischargechamber 1 carry metal coatings 2a and 2b, e.g. metal plates or sheets,on which the electrodes 3a and 3b are mounted.

The chamber 1 is made of an insulating material, e.g. a ceramic or aplastic material. Suitable plastics include, for example, Plexiglas,polypropylene, tetrafluoroethylene of SOLEF (PVDF). A wire grid 4 isincorporated in the lateral walls of the chamber 1 at a small distance(some millimeters) from the inner surface, which extends on both sides,i.e. upward and downward, to the level of the metal plates 2a and 2b.

It has been found that upon rapid application of a voltage to theRogowski electrodes a corona discharge takes place in this embodimentprior to the main discharge on the surface of the lateral walls, alongthe wire grids 4 inside the laser chamber 1; this corona discharge emitsUV light and ensures very uniform discharge.

If the discharge chamber is made from a transparent insulating material,the wire grids 4 permit observation of the gas discharge from outside.Another possibility is to replace the wire grids 4 by metal foils orplates 5, which can also be mounted on the outside, as can be seen,e.g., from the lateral view shown in FIG. 2. It should be noted,however, that the insulating layer betwen wire screen 4 or foil andinner surface of the wall of the discharge chamber 1 must not be toothick. For reasons of mechanical stability, it is therefore preferableto incorporate the wire screens 4 or the foils into the walls asindicated above. This also solves the problems of insulation andattachment, and the design becomes particularly simple and cheap.

In a corresponding design for high pulse frequency, the laser gas israpidly circulated by means of fans 6 and passed through a cooler 7, asshown in FIG. 3. The gas circulation and cooling system 6 and 7 isarranged adjacent to the wall of the discharge chamber 1 which carriesan electrode 3b. The arrangement of the gas circulation and coolingsystem is also depicted in lateral view in FIG. 2. In the region whichis not covered by the electrode 3b, the partition wall with metalcoating 2b is provided with openings 8 which permit the laser gas to besupplied on one side of the electrode and drawn off on the other side.

Such an embodiment is depicted in FIG. 4, which shows such openings 8 inthe partition wall along the electrode 3b. Instead of a number of axialfans, it is also possible to use a radial fan of appropriate length forthis application. In this case the insulating partition wall can beomitted, so that the electrode is carried alone by metal plate 2a whichserves as partition. To increase the corona discharge, a conductingconnection can be provided between the two wire grids 4 and one of thetwo metal plates 2b (FIG. 3).

For various applications involving high mechanical stress on the laser,it has been found useful to execute the laser part and the fan part pluscooler in modular construction. The two parts can be separated from eachother by loosening clamps. This version of the present invention makesmaintenance particularly easy.

FIG. 5 shows a laser of this type with discharge capacitors and sparkgap for initiating the gas discharge in the cross section. Because ofthe symmetrical design of the laser chamber, the capacitors and thespark gap can be arranged symmetrically. This results in a dischargecircuit of low inductivity and a very short discharge time. These factsalso contribute to the very homogeneous gas discharge of the laseraccording to the invention, which in turn results in highreproducibility of the pulses that are generated and in correspondinglygood radiation properties.

It is, of course, not necessary that the laser chamber and the chamberfor fan and cooler are of equal size. The relative sizes have to beadapted to the respective requirements (pulse frequency or flow velocityand cooling capacity as well as gas volume).

We claim:
 1. An apparatus for the generation of laser radiationconsisting essentially ofa discharge chamber made from an insulatingmaterial, said discharge chamber having two opposite walls and twolateral walls made from an insulating material which enclose an interiorspace containing an optical resonator, said opposite walls beingprovided with metal coatings on which two discharge electrodes aremounted, said discharge chamber being provided with conductingstructures which are insulated from the interior space and extendbetween said two discharge electrodes on both sides thereof and betweenthe levels of the metal coatings in said opposite walls, whereby bymeans of said discharge electrodes and conducting structures a gasdischarge can be produced transverse to the optical resonator initiatedby UV preionization arising from a corona discharge characterized inthat the conducting structures are arranged on or within both thelateral walls of the discharge chamber and are insulated from theinterior space by said lateral walls of the discharge chamber andwherein a gas circulation and cooling system are disposes in a chamberarranged adjacent to one of said opposite walls said opposite walladjacent to the chamber containing the gas circulation and coolingsystem being provided with openings through which the laser gas flows.2. The apparatus as claimed in claim 1, wherein the metal coatingconsists of metal plates or sheets.
 3. The apparatus as claimed in claim2, wherein a conducting connection exists between the two conductingstructures and one of the two metal coatings.
 4. The apparatus asclaimed in claim 2, wherein wire grids are used as conductingstructures.
 5. The apparatus as claimed in claim 2, wherein metalplates, sheets, or foils are used as conducting structures.
 6. Theapparatus as claimed in claim 2, wherein the conducting structures areembedded in the lateral walls of the discharge chamber at a distancefrom the inner surface of the discharge chamber which is sufficient forinsulation.
 7. The apparatus as claimed in claim 2, wherein theconducting structures are mounted on the outside of the dischargechamber.
 8. The apparatus as claimed in claim 1, wherein a conductingconnection exists between the two conducting structures and one of thetwo metal coatings.
 9. The apparatus as claimed in claim 8, wherein wiregrids are used as conducting structures.
 10. The apparatus as claimed inclaim 8, wherein metal plates, sheets or foils are used as conductingstructures.
 11. The apparatus as claimed in claim 8, wherein theconducting structures are embedded in the lateral walls of the dischargechamber at a distance from the inner surface of the discharge chamberwhich is sufficient for insulation.
 12. The apparatus as claimed inclaim 1, wherein wire grids are used as the conducting structures. 13.The apparatus as claimed in claim 12, wherein the conducting structuresare embedded in the lateral walls of the discharge chamber at a distancefrom the inner surface of the discharge chamber which is sufficient forinsulation.
 14. The apparatus as claimed in claim 1, wherein metalplates, sheets or foils are used as the conducting structures.
 15. Theapparatus as claimed in claim 14, wherein the conducting structures areembedded in the lateral walls of the discharge chamber at a distancefrom the inner surface of the discharge chamber which is sufficient forinsulation.
 16. The apparatus as claimed in claim 1, wherein theconducting structures are embedded in the lateral walls of the dischargechamber at a distance from the inner surface of the discharge chamberwhich is sufficient for insulation.
 17. The apparatus as claimed inclaim 1, wherein the conducting structures are mounted on the outside ofthe discharge chamber.
 18. The apparatus as claimed in claim 1, whereinthe chamber wall of insulating material which carries an electrode isomitted and wherein the partition wall is formed by the metal plate orthe metal sheet.
 19. The apparatus as claimed in claim 1, wherein thedischarge chamber and the gas circulation and cooling system chamberform two separate gas-tight connected units.
 20. The apparatus of claim1 wherein the discharge chamber has a substantially rectangularconfiguration.